1. Field of the Invention
The present invention relates to an ink jet head, an ink jet printer and a method for manufacturing an ink jet head. More particularly, the present invention relates to an ink jet head, an ink jet printer and a method for manufacturing an ink jet head, in which multiple ink nozzles are arranged in a sub-scan direction in each of a plurality of nozzle arrays arranged in a main scan direction.
2. Related Background Art
As one of ink jet printers, an ink jet printer in which an ink jet head mounted on a carriage is reciprocally moved in a main scan direction and a recording medium is moved in a sub-scan direction, and recording is performed on the recording medium by using an ink droplet discharged from the ink jet head has conventionally been known.
In the ink jet head used in the above-mentioned printer, ink nozzles are arranged in the sub-scan direction to form a nozzle array, and, in general, a plurality of nozzle arrays are arranged in the main scan direction to permit color recording. Among these heads, as disclosed in Japanese Patent Application Laid-open No. 2001-171119, there is an ink jet head in which nozzles for discharging color ink are disposed symmetrically in a left-and-right direction and offset by a half pitch, which head has excellent performance for performing reciprocal printing.
Among these ink jet heads, as disclosed in Japanese Patent Application Laid-open No. H11-5307, an ink jet head having vaporization suppressing grooves in the vicinity of discharge ports in order to suppress vaporization of ink from the discharge ports and to prevent unstable discharging is known. Further, in a method for manufacturing an ink jet head in which, after resin is coated on a mold for forming flow paths, the mold is removed to form the flow paths, a groove is provided in a nozzle surface (referred to as “face surface” hereinafter) to make a thickness of the resin uniform, as disclosed in Japanese Patent Application Laid-open No. H09-001809.
By the way, in a case where the recording is performed by using the ink jet head, following a main ink droplet, minute ink droplet or droplets may be generated delayed from the main ink droplet. Further, when the main ink droplet strikes against a recording medium, due to an ink rebound phenomenon, minute ink droplet or droplets may be generated. These minute ink droplets are called “ink mist” and are adhered to the face surface by an air flow caused by the movement of the carriage and the liquid droplet itself. Further, the ink mist adhered to the face surface may be gathered to create ink mass (referred to as “face wet region” hereinafter). If the face wet region appears in the vicinity of the discharge port, a discharging direction of the discharged ink droplet may be unstable to cause so-called dot mis-alignment that an ink dot cannot strike against a desired position. To avoid this, a technique in which the face surface is formed as a water-repelling surface to reduce the amount of the ink mist remaining in the vicinity of the discharge port, thereby minimizing the influence affecting upon the discharging performance, has been proposed.
However, the Inventor discovered that, if the ink mist is adhered to the water-repelling surface collectively, the following phenomenon may be generated.
That is to say, in a case where the face wet region is generated for example by extremely increasing driving frequency for performing the ink discharging, when a diameter of the face wet region reaches about 100 μm or more, the ink mist can easily be moved on the face surface. Thus, the face wet region will be combined with adjacent face wet region(s) to create a greater face wet region due to an inertia force generated during the reciprocal scanning operations of the head. If so grown greater face wet region exists on the face surface, as the case may be, the face wet region covers or closes the discharge ports in a condition that bubbles exist in the nozzles, non-discharge occurs during the recording. It is feared that such a phenomenon is generated also in the arrangements disclosed in the above-mentioned Japanese Patent Application Laid-open Nos. H11-005307 and H09-001809.
Although this problem can be solved by performing a recovery process in which the face surface is cleaned by a blade and the like and the ink is sucked, if the recovery process is carried out frequently during the recording operation, the recording speed will be sacrificed. Since it is expected that the number of nozzles will increase in future ink heads as compared to conventional ink heads due to higher image quality and higher printing speed, the above-mentioned problem will be more remarkable. Thus, there is a need for realizing new solving methods different from the conventional ones.